Ultra-thin interposer assemblies with through vias

ABSTRACT

A 3D interconnect structure comprising an ultra-thin interposer having a plurality of ultra-high density of through-via interconnections defined therein. The 3D interposer electrically connects first and second electronic devices in vertical dimension and has the same or similar through-via density as the first or second electronic devices it connects. The various embodiments of the interconnect structure allows 3D ICs to be stacked with or without TSVs and increases bandwidth between the two electronic devices as compared to other interconnect structures of the prior art. Further, the interconnect structure of the present invention is scalable, testable, thermal manageable, and can be manufactured at relatively low costs. Such a 3D structure can be used for a wide variety of applications that require a variety of heterogeneous ICs, such as logic, memory, graphics, power, wireless and sensors that cannot be integrated into single ICs.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 61/409,221, filed 2 Nov. 2010, which isincorporated herein by reference in its entirety as if fully set forthbelow.

BACKGROUND

1. Field

The various embodiments of the present invention relate to ultra-smallpitch interconnect structures comprising of ultra-thin interposershaving ultra-high density through vias defined therein.

2. Description of Related Art

The increasing number of smart and mobile phone applications, includingvideo streaming, 3D graphics, camera-functions, and gaming, are drivingthe demand for logic to memory bandwidth (BW) at increasing levelswithout an increase in power consumption. Bandwidth is defined as bitrate per pin or I/O and the number of I/Os. Bit rate per pin isinfluenced by many factors, the most important factor beinginterconnection length between two devices. The main elements thatinfluence bandwidth, therefore, are (1) the number of parallelinterconnections between a logic and memory (IC) devices in a givenarea, referred to as I/O density, determined by the pitch ofinterconnections and (2) the length of such interconnections between thelogic and memory devices.

FIG. 1 illustrates various 3D packaging schemes of the prior art and anillustration of an exemplary embodiment of the present invention (FIG. 1e). Briefly described, the packaging schemes are, for example, asystem-in-package (SIP) structure (FIG. 1 a), a package-on-package (POP)structure (FIG. 1 b), a face-to-face (F2F) structure (FIG. 1 c), and alogic on bottom stack (FIG. 1 d) structure. The logic on bottom stackstructure is a next generation configuration that utilizes 3D ICs withcomplex and expensive through silicon vias (TSVs).

The wire-bonded SIP and POP structures are limited in the number ofchip-to-chip interconnections and the interconnection length, preventingthese structures from providing high bandwidths without a significantincrease in power consumption. The F2F structure achieves finer-pitchI/Os and thus increases the number of chip-to-chip interconnections,however, the design is limited to two chips and therefore cannot bescaled to multiple chips or sub-systems.

Silicon interposers with very high I/Os at finer pitches offer potentialsolutions to these problems of the prior art configurations, as multipleICs may be placed side by side on the silicon interposer and connectedthrough lateral re-distribution layer wiring. Such a structure has twolimitations, however. First, this structure is very expensive tomanufacture, attributed to the small number of interposers produced from200-300 mm wafers as well as the expensive back-end-of-line (BEOL)processes. The second limitation is related to the electrical signaldelay, due to both electrical lossiness of silicon as well the long wirelengths with high resistance.

An entirely new, complex, and expensive technology, called “3D ICs withTSVs”, is being developed worldwide in an effort to achieve ultra-highbandwidth using TSVs fabricated within logic, memory, and other ICs, andstacking these devices one on top of the other to enable ultra-finepitch and ultra-short interconnections, as illustrated in FIG. 1 d.However, this form of multi-die stacking with TSVs imposes greatchallenges in forming TSVs within complementary metal oxidesemiconductor (CMOS) chips, power delivery, testability, reliability,and thermal management of logic chip, all of which remain major barriersin achieving high bandwidth for 3D ICs. Additionally, organic, ceramic,and glass carriers having conductive through vias have been described inprior art, however, they do not operate at high bandwidths because ofcoarse pitch and long interconnections. The interconnect structure ofthe present invention, a three-dimensional (3D) interposer, achieves thesame ultra high density of interconnections at ultra short lengths, verysimilar to TSVs within the logic and memory devices. Such a structureserves many applications for heterogenous stacking of ICs that cannot beintegrated into a single IC. One such application is for providing highbandwidth, comparing favorably over 3D ICs with TSVs, as it is scalable,testable, thermal manageable, and can be manufactured at lower costs.

BRIEF SUMMARY

Exemplary embodiments of the present invention provide a 3D interposerinterconnect structure, comprising an interposer having a first side anda second side, the interposer being about 20 to about 200 micrometers inthickness; and a plurality of through-vias defined within the interposerextending at least from the first side to the second side of theinterposer, wherein the thickness of the interposer to via diameteraspect ratio is about 1:1 to about 10:1; and wherein the interposerelectrically connects first and second electronic devices on either sideof the through-vias and has the same or substantially the samethrough-via interconnect density as the first and second electronicdevices it connects.

Other exemplary embodiments of the present invention provide a testableinterposer interconnect structure, comprising an interposer having afirst side and a second side; and a plurality of through vias definedwithin the interposer extending at least from the first side to thesecond side of the interposer; wherein the interposer electricallyconnects first and second electronic devices on either side of thethrough-via and has the same or substantially the same through-viainterconnect density as the first and second electronic devices itconnects; and wherein the interposer comprises test pads on the firstand second sides of the interposer to enable testing of electronicdevices attached and electrically connected to at least one of the firstand second sides of the interposer.

Further exemplary embodiments of the present invention provide ease ofthermal management interposer interconnect structure, comprising: aninterposer having a first side and a second side; and a plurality ofthrough-vias defined within the interposer extending at least from thefirst side to the second side of the interposer; and wherein theinterposer electrically connects first and second electronic devices oneither side of the through-via and has the same or substantially thesame through-via interconnect density as the first and second electronicdevices it connects; and further wherein the first and second electronicdevices are connected by a plurality of electrically and thermallyconducting through-vias, wherein the plurality of through-vias aredistributed within the interposer and provide localized thermalisolation or thermal conduction between the first and second electronicdevices.

Additional exemplary embodiments of the present invention provide ascalable interposer interconnect structure, comprising: an interposerhaving a first side and a second side; and a plurality of through viasdefined within the interposer extending at least from the first side tothe second side of the interposer, wherein the thickness of theinterposer to via diameter aspect ratio is about 1:1 to about 10:1;wherein the interposer electrically connects electronic devices and hasthe same through-via interconnect density as the electronic devices itconnects; and wherein a plurality of electronic devices are attached tothe first side of the interposer in a side-by-side configuration.

FIGURES

FIG. 1 a illustrates a prior art system-in-package interconnectstructure embodiment.

FIG. 1 b illustrates a prior art package-on-package interconnectstructure embodiment.

FIG. 1 c illustrates a prior art face-to-face package interconnectstructure embodiment.

FIG. 1 d illustrates a prior art logic-on-bottom stack interconnectstructure embodiment.

FIG. 1 e illustrates an exemplary embodiment of an interconnectstructure of the present invention comprising a 3D interposer defining aplurality of through vias.

FIG. 2 graphically illustrates the bandwidth of the interconnectstructure embodiments illustrated in FIGS. 1 a-1 e.

FIG. 3 illustrates another exemplary embodiment of the interconnectstructure of the present invention comprising an interposer defining aplurality of through vias.

FIG. 4 illustrates a top view of the interconnect structure illustratedin FIG. 3.

FIGS. 5 a-5 d illustrate various exemplary embodiments of theinterconnect structure of the present invention.

FIG. 6 illustrates a method of integrating and testing the interconnectstructure of the present invention.

FIG. 7 illustrates a schematic model of through vias in a 3D glassinterposer.

FIG. 8 graphically illustrates an insertion loss comparison for throughvias in a glass interposer utilizing different glass and polymericcompositions

FIGS. 9 a and 9 b illustrate a cross-sectional view of a copper-filledTPV and a conformal copper through via, respectively.

FIG. 10 graphically illustrates the effect of through-via metallizationon its insertion loss.

FIG. 11 provides a cross-sectional image of through vias in a polymerlaminated glass.

FIGS. 12 a and 12 b provide a top-view image and a cross-sectional viewimage, respectively, of a plurality of through vias.

FIG. 13 provides an image of a plated fine pitch via in glass.

FIGS. 14 a and 14 b provide images showing the definition of fine lineand space features of the through vias down to 10 μm and 5 μm,respectively.

FIG. 15 illustrates the process flow for glass test vehicle fabrication.

FIGS. 16 a-16 c illustrates a fabricated glass test vehicle.

FIG. 17 graphically illustrates measurement and simulation plots of aring resonator in a glass test vehicle.

FIG. 18 a illustrates a cross-sectional view of a CPW line tothrough-via transition structure.

FIG. 18 b graphically illustrates the insertion loss plot of the CPWline to through-via transition structure illustrated in FIG. 18 a.

FIG. 19 illustrates a schematic model of a TPV in a silicon interposer.

FIGS. 20 a and 20 b graphically illustrate insertion loss and far-endcrosstalk plots, respectively, for through vias in CMOS grade andpolycrystalline based silicon interposers.

FIGS. 21 a and 21 b graphically illustrate insertion loss and far-endcrosstalk plots, respectively, for through vias with different sidewallliner thicknesses.

FIGS. 22 a and 22 b graphically illustrate insertion loss and far-endcrosstalk plots, respectively, for through vias with differentdiameters.

FIG. 23 illustrates the process flow for through-via fabrication.

FIG. 24 provides top and bottom views of through vias fabricated bythree types of lasers.

FIG. 25 illustrates a cross-sectional view of a through-via drilled insilicon by a UV laser.

FIG. 26 illustrates a cross-sectional view of a polymer filledthrough-via in silicon.

FIG. 27 illustrates the process flow for silicon test vehiclefabrication.

FIG. 28 illustrates a cross-sectional view of fine line structure onpolymer laminated polycrystalline silicon.

FIG. 29 graphically illustrates an insertion plot for a CPW line.

FIG. 30 illustrates a thermally managed interconnect structure of thepresent invention for a low power logic component.

FIG. 31 illustrates a thermally managed interconnect structure of thepresent invention for a high power logic component.

FIG. 32 illustrates a scalable interconnect structure of the presentinvention in a side-by-side configuration.

FIG. 33 illustrates an interconnect structure of the present inventionconfigured for a cell phone camera application.

FIG. 34 illustrates a method for fabricating TSVs through a singlecrystalline silicon interposer.

FIGS. 35 a and 35 b illustrate a typical top and bottom view,respectively, of a circular TSV.

FIG. 36 illustrates a top view of a wafer inspected for a uniform viasize.

FIG. 37 illustrates the top view and micro-section images of arepresentative TSV daisy chain with about 65 μm diameter vias

DETAILED DESCRIPTION

Referring now to the figures, wherein like reference numerals representlike parts throughout the several views, exemplary embodiments of thepresent invention will be described in detail. Throughout thisdescription, various components can be identified as having specificvalues or parameters, however, these items are provided as exemplaryembodiments. Indeed, the exemplary embodiments do not limit the variousaspects and concepts of the present invention as many comparableparameters, sizes, ranges, and/or values can be implemented.

It should also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an,” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,reference to a component is intended also to include composition of aplurality of components. References to a composition containing “a”constituent is intended to include other constituents in addition to theone named. Also, in describing the preferred embodiments, terminologywill be resorted to for the sake of clarity. It is intended that eachterm contemplates its broadest meaning as understood by those skilled inthe art and includes all technical equivalents which operate in asimilar manner to accomplish a similar purpose.

Values may be expressed herein as “about” or “approximately” oneparticular value, this is meant to encompass the one particular valueand other values that are relatively close but not exactly equal to theone particular value. By “comprising” or “containing” or “including,” itis meant that at least the named compound, element, particle, or methodstep is present in the composition or article or method, but does notexclude the presence of other compounds, materials, particles, methodsteps, even if the other such compounds, material, particles, methodsteps have the same function as what is named.

It is also to be understood that the mention of one or more method stepsdoes not preclude the presence of additional method steps or interveningmethod steps between those steps expressly identified. Similarly, it isalso to be understood that the mention of one or more components in acomposition does not preclude the presence of additional components thanthose expressly identified.

As used herein, the terms “interconnect,” “interconnect structure,” and“interposer interconnect structure” may be used interchangeably andrefer to connecting devices to form a package, module, sub-system orsystem.

The various embodiments of the present invention provide an interconnectstructure comprising an ultra-thin interposer having a plurality ofultra-high density through-via interconnections defined therein. Such aninterposer is referred to as a “3D interposer” as it interconnects twoor more devices on either side of the interposer with an unprecedenteddensity of interconnections between the two or more devices. Theinterposer of the present invention thus electrically connects the firstand second set of devices at the same or similar through-via density asin the first and second electronic devices. In prior art embodiments,the through vias in the interposer or package were generally of the samesurface-mount pitch as the board, typically from 400-1000 microns. The3D interposer of the present invention provides short, through-viainterconnections, not at the board pitch of 400-1000 microns, but atdevice pitch of 10-30 microns. As illustrated in FIG. 2, the variousembodiments of the interconnect structure increases bandwidth betweenthe two electronic devices as compared to other interconnect structuresand does so by (1) utilizing an ultra-thin interposer, thereforeresulting in ultra-short interconnections, and (2) achieving ultra-finepitch conductive through-via structures using novel process methods tofabricate such interposers. Further, the interconnect structure of thepresent invention is scalable, testable, thermal manageable, and can bemanufactured at relatively low costs.

Referring to FIG. 3, there is shown an exemplary embodiment of aninterconnect structure 100 of the present invention. As illustrated, theinterconnect structure comprises an interposer 105 having a first side115 and a second side 120. The interposer 105 is ultra-thin and is lessthan about 100 micrometers in thickness. In exemplary embodiments, theinterposer 105 is less than about 800 micrometers in thickness, and morespecifically about 20-100 micrometers in thickness. In preferredembodiments, the interposer is about 30 micrometers in thickness. Theinterposer 105 can be made of many substrate materials, for example,glass, silicon, ceramic, polymer-glass laminates, and flexible polymers,and can be of many shapes, for example wafer, small square orrectangular panels, or large panel shapes. In exemplary embodiments, theinterposer 105 is made of glass or any other substrate with a thermalconductivity as low as about 5 W/mK or as high as about 125 W/mK, orhigher, as in the case of silicon. Glass presents several advantages,namely, silicon-matched coefficient of thermal expansions (CTE),excellent surface flatness, dimensional stability, high electricalresistivity, and thin and large panel availability. These propertiesenable glass to isolate heat between the two electronic devices itconnects on either side. In other exemplary embodiments, the interposer105 is made from silicon or any other substrate with a thermalconductivity of about 125 W/mK, which is also an advantageous materialas it can provide thermal conduction in both x and y directions and canbe in either in single crystalline or polycrystalline form.

A plurality of ultra-small through vias 110 can be defined within theinterposer 105 such that each of the through vias 110 extends from thefirst side 115 to the second side 120 of the interposer 105. Theinterposer thickness to through-via diameter size, referred to as the“aspect ratio,” can range from about 1:1 to about 10:1. Morespecifically, the through vias 110 are ultra-small and can range fromabout 1-25 micrometers in diameter at about 3-50 micrometers in pitch.In exemplary embodiments, the through vias 110 are about 1-20micrometers in diameter at about 3-40 micrometers in pitch. The vias areelectrically and thermally conducting, and are distributed within theinterposer such that they provide localized thermal isolation or thermalconduction between the first and second electronic devices. FIGS. 30 and31 illustrate a thermally managed interconnect structure of the presentinvention for both a low and high power logic component, respectively.The through vias 110 can be metalized in such a way that themetallization provides die pad surfaces 135 that correspond to each ofthe vias 110 on both the first side 115 and the second side 120 of theinterposer 105. Specifically, the through vias 110 can be metalized witha highly-conductive metal, for example copper. Further, the through vias110 can also be metalized with a polymer liner or a metal seeding liner.The die pads 135 that are formed on the first 115 and second sides 120of the interposer 105 can electrically connect devices using solder,copper bumps with solder caps, copper to copper bonding, adhesivebonding, metallurgical bonding, non-conductive bonding, or combinationsthereof.

A first electronic device 125 can be attached to the first side 115 ofthe interposer 105 and a second electronic device 130 can be attached tothe second side 120 of the interposer 105. In exemplary embodiments, thefirst electronic device 125 can be single or stacked memory IC devices,and the second electronic device 130 can be a logic IC device ordevices. It shall be understood that other electronic devices can alsobe used as the first electronic device 125 and/or the second electronicdevice 130. For example, an exemplary embodiment of the present 3Dinterposer can be a digital camera for cell phones, with an image sensorchip on one side and an Asic chip on the other side of the interposer,as illustrated in FIG. 33. The interposer 105 and the through vias 110work to electrically connect the first electronic device 125 and thesecond electronic device 130, and have substantially the samethrough-via interconnect density as the first electronic device 125 orthe second electronic device 130 it connects. This enables the first 125and second 130 electronic devices to communicate at bandwidth speeds ofat least about 10 GB/s, as illustrated in FIG. 2. It shall be understoodthat while the interconnect structure 100 of the present invention iscapable of achieving such high bandwidth speeds, the interconnectstructure 100 is scalable (e.g., to decrease bandwidth speed) to meetthe demands of specific applications.

Unlike many prior art embodiments, the first 125 and second 130electronic devices can be connected to the interposer 105 in a face toface configuration (i.e., the active device surface is adjacent andfirst 115 and second 120 sides of the interposer 105). Further, asillustrated in FIG. 3, electronic devices having different I/O padlayouts and sizes can also be connected through the use of blind vias140 and conductor traces 145 defined within polymer-metal redistributionlayers deposited on the first side 115 and second side 120 of theinterposer 105.

FIG. 4 illustrates a top view of the interconnect structure 100 showingthe first electronic device 125 above the interposer 105, and the secondelectronic device 130 below the interposer 105. As illustrated, thefirst electronic device 125 is of a different pad size and configurationthan the second electronic device 130, and they are connected withthrough vias 110, blind vias 140, and conductor traces 145. FIG. 5 showsvarious exemplary embodiments of the interconnect structure 100,illustrating the versatility in electronic devices and stackingconfigurations. It shall be understood that not all embodiments of theinterconnect structure 100 of the present invention are illustrated andthus, the interconnect structure 100 is in no way intended to be limitedsolely to these figures. For example, third and fourth electronicdevices can be stacked on the first 125 and second 130 electronicdevices, respectively to create a 3D configuration. In stackingembodiments, through vias are defined within the first 125 and second130 electronic devices, as well as the interposer, to facilitatecommunication with the third and fourth electronic embodiments.Contrastingly, in embodiments that connect first 125 and second 130electronic devices only (as illustrated in FIG. 3), at least one, if notboth, of the electronic devices do not have through vias, which isdistinguishable from many prior art embodiments.

The exemplary embodiments of the interconnect structure 100 provide manybenefits over the prior art. For example, the interconnect structure 100of the present invention offers the smallest interconnections (e.g., theplurality of vias 110) that run through the best electrically-insulatingsubstrate (e.g., the glass interposer 105), which reduces latency,signal loss, and power. Further, glass interposers have extremely lowelectrical loss with respect to signal propagation. This characteristicbecomes critical in scenarios where signal lines become longer than afew microns, such as with interposers. Further, glass interposerseliminate the need for through-silicon-vias (TSVs) in the logic IC,which substantially, if not completely, eliminates complications of 3DICs discussed above. Additionally, the double-side mounting ofelectronic devices to the interposer 105 allows for the testability ofthe interposer 105 before and after integrating each of the electronicdevices. This integration and testing method is illustrated in FIG. 6.The first step 605 is interposer fabrication with through vias and RDLconstruction (chip-last); the interposer is tested at this stage. Thesecond step 610 is the assembling, mounting, and testing of the firstelectronic device; the third step 615 is the assembling, mounting, andtesting of the second electronic device. This process alleviates theKnown Good Die (KGD) concerns in 3D IC integration because each die canbe tested after assembly to the interposer. Further, the interconnectstructure 100 of the present invention provides an inclusive systemlevel integration approach allowing 3D ICs to be integrated with andincrease the number of dies. The 3D interposer of the present inventionis scalable for increased number of dies, not only above and below theinterposer but also side by, as illustrated in FIG. 32. This is incontrast to 3D ICs with TSV where, multiple dies over 4 are a problem inthe prior art. Furthermore, the interconnect structure of the presentinvention enables the interposer 105 and the package can be one and thesame, in contrast to today's 3D ICs that attach to interposers, whichthen attach to packages before being assembled onto boards, thuslowering the packaging costs by eliminating complex interposers andpackages that are needed for current 3D ICs.

GLASS INTERPOSER EXAMPLES Example #1 Electrical Modeling of TPVs

The effect of different through-package-via (TPV) formation processes oninsertion loss and crosstalk was studied using electromagnetic (EM)simulations. TPVs were modeled and simulated in CST Microwave Studio™(CST-MWS)—a 3D full-wave Electromagnetic (EM) simulator. The systemresponse was studied up to about 10 gigahertz (GHz). The conceptual TPVmodel is illustrated in FIG. 7. The model comprises a signal via (markedas ‘S’ in FIG. 7) surrounded by two ground vias (marked as ‘G’ in FIG.7). The signal via was excited by discrete ports on its top and bottomsurfaces. Two types of glass substrates were considered in thisstudy—Glass 1 (a low CTE borosilicate glass) and Glass 2 (a high CTEglass). The glass substrate was 180 μm thick and had a 15 μm thicksurface polymer liner on its top and bottom surfaces. Two types of linermaterial were also used—Polymer 1 and Polymer 2. The TPVs were about 30micrometers (μm) in diameter and about 60 μm in pitch. The TPVs weremodeled as completely filled with copper. FIG. 8 shows the insertionloss comparison for the TPVs in different glass and liner materialcombinations. Notably, changing the glass or liner material had littleeffect on the TPV loss.

Two types of TPV metallization options were also studied, fully filledCu and partially or conformally filled Cu, as illustrated in FIG. 9.Glass 2 and Polymer 2 were chosen as the substrate and liner material.The via diameter and pitch were about 30 μm and about 60 μmrespectively. The glass thickness was about 180 μm. FIG. 10 shows thesimulated insertion loss for the two metallization options. Theconformal Cu TPV has almost identical loss behavior as the completely-Cufilled TPV. This can be attributed to skin effect. As demonstrated, anycombination of the glass and polymer materials considered in thisexample can lead to good electrical performance of the TPVs. ConformalCu TPVs exhibit similar performance as Cu filled TPVs. However, theconformal TPVs are expected to exhibit better thermo-mechanicalreliability behavior.

Example #2 Mechanical Design and Modeling of TPVs

Finite Element (FE) models were developed to provide design guidelinesfor TPV structures in glass interposers. Various combinations of glassand polymer materials were studied in terms of interfacial shear stress(σ_(xy)) and axial stress in polymer (σ_(x)) as metrics representingfailure mechanisms for delamination or cracking, respectively. Table 1shows the material properties used in the FE models, and the models usedin the study were subjected to a standard thermal load cycle of about−55 to 125° C.

TABLE 1 Young's Poisson's CTE Stress free Temp. Modulus (GPA) Ratio(ppm/° C.) (° C.) Glass 1 77 0.22 3.8 25 Glass 2 71 0.24 8.5 25 Polymer1 1.83 0.3 67 232 Polymer 2 6.9 0.3 31 120 Copper 121 0.3 17.3 25

Example #3 Fabrication of Ultrafine Pitch TPVs

The biggest challenge with glass interposers is the formation of smallvias at fine pitch TPVs (<50 μm) in a cost effective way. Hence there isa need to explore thin glass substrates which will enable ultrafinepitch TPV formation in a faster way. This example focused on excimerlaser via formation on ultrathin glass substrates (<200 μm). To enhancethe knowledge of excimer laser micro fabrication, two types of drillingtechniques—single hole drilling and multiple drilling using maskprojection were investigated.

In the case of the single hole drilling, via formation using excimerlasers was carried out on double side polymer-laminated, 175 μm thinBorosilicate glass (BSG). The 50 μm pitch vias demonstrated in the priorart have a conical profile with a flare at the entrance of the via. Suchan artifact has been reported in literature and is attributed to laserbeam reflections at the glass surface. Using polymer-laminated glass,improved via profiles were obtained with almost vertical and smooth sidewalls, as illustrated in FIG. 11. The entrance and exit diametersobtained were 27 μm and 15 μm, respectively. The polymer liner on theglass surface helped minimize the laser beam reflections, thus enablingsharp via corners.

Thus far, the throughput of via drilling in a glass substrate has beenone of the crucial problems in 3D glass interposer mass production,because conventional laser ablation has been a serial process andablation rates in glass are much lower than in polymers. This experimentexplored a parallel via ablation process using a mask projectiontechnique. As one of the examples of multiple drilling, a mask with a33×33 array pattern (1089 holes) was used. FIG. 12 a shows the top viewoptical image of TPVs formed in 55 μm ultrathin BSG. More than onethousand uniform vias at a pitch of 30 μm were obtained simultaneouslyin one laser ablation process. FIG. 12 b shows the SEM micrograph of asplit cross section of the vias. The entrance and exit diametersobtained were approximately 19 μm and 6 μm, respectively. The obtainedside walls were smooth and the vias were formed within 10 seconds. FIG.13 provides an image of a plated fine pitch via in glass. The maskprojection process thus has tremendous potential for low cost viaformation of small diameter vias at fine pitch in ultrathin glass.

Example #4 Fine Line Wiring on Glass

Wiring with small line width and line spacing helps interconnect severalI/Os between ICs and 3D ICs using a minimum number of routing layers.Fine line wiring on organic packages has been studied using apanel-based, wet processing approach. Wiring on silicon is achievedusing wafer-based lithography process that helps achieve feature sizesless than about 1 μm. The favorable dimensional stability and smoothsurface of glass facilitates this fine line wiring. However, direct wetmetallization on glass has been a challenge due to surface chemistry ofglass and its interaction with metals. The presence of a surfacepolymer, however, on glass facilitates metallization. The glass TPV sidewalls were subjected to direct metallization using wet electrolesscopper deposition. A semi-additive plating (SAP) approach was usedwherein the fine lines and the through vias were metalizedsimultaneously. Fine-line and space definitions with dimensions of about10 μm or less were achieved on polymer-laminated glass cores using dryfilm and liquid photo-resists. FIGS. 14 a and 14 b show the definitionof fine line and space features down to about 10 μm using about 15 μmthin dry film negative photo-resist. Fine line definition down to about5 μm was achieved using negative liquid photoresist. After patterning,the features were electroplated with copper to a height of about 5 μm toabout 10 μm. Post electroplating, the seed layer was removed afterstripping the photo-resist.

Example #5 Glass Test Vehicle Demonstrator

A glass test vehicle was designed and fabricated to characterize thesubstrate and TPVs in glass. FIG. 15 shows the process flow used forfabricating the test vehicle. A 150 mm×150 mm square glass panel with athickness of about 180 μm was used for the test vehicle demonstrator.BSG with polymer1 was used for the initial test vehicle fabrication. Akey fabrication challenge was the handling of ultrathin glass substratesduring the different stages of processing. Glass, being a brittlematerial, is prone to cracking. The double-side polymer laminationhelped enhance the handling of glass by acting as a stress relief layer,providing mechanical support to the glass. Through-vias were formed withentrance and exit diameters of about 130 μm and about 90 μm respectivelyusing laser ablation. Metallization of TPVs and on the surface of glassinterposer was carried out using copper as metal and SAP (semi additiveplating) approach. The resulting two metal layer structure is shown inFIG. 16 a-c.

Ring resonators were designed to extract the dielectric constant andloss tangent of the interposer. FIG. 17 shows the measured and simulatedresponse of the ring resonator up to 20 GHz. The electrical propertiesof the glass interposer, as shown in Table 2, were extracted from themeasurement and simulation data. The interposer demonstrated goodelectrical properties with a low dielectric constant and loss tangent upto 19.4 GHz. Some structures were designed and fabricated tocharacterize the electrical characteristics of the interconnections(lines and TPVs) in glass interposer. FIGS. 16 c and 18 a show the topview and the cross-sectional view of a CPW line to TPV transitionstructure, respectively. The comparison between the measured andsimulation data for this structure is shown in FIG. 18 b. It wasobserved that the simulation results correlate well with the measurementresults. The interconnection has low insertion loss (less than 0.15 dB)until 9 GHz.

TABLE 2 n Freq. (GHz) DK(ε_(r)) DF(tanδ) 1 2.44 4.73323  0.002861 2 4.884.712096 0.002852 3 7.28 4.776466 0.001906 4 9.72 4.754924 0.001814 512.2 4.742063 0.001963 6 14.6 4.769319 0.001979 7 17 4.788918 0.002104 819.4 4.803689 0.001806

POLYCRYSTALLINE SILICON 3D INTERPOSER EXAMPLES Example #1 ElectricalModeling of TPVs/TSVs

Electromagnetic modeling and simulation results were presented tocompare the electrical performance of through silicon vias (TSVs) andTPVs in polycrystalline-silicon interposers. Parametric studies of theTPV diameter and sidewall liner thickness on electrical performance isalso presented.

TPVs were modeled and simulated for their electrical characteristics bymeans of 3D full-wave Electromagnetic (EM) simulations. CST MicrowaveStudio™ (CST-MWS) was used as a 3D full-wave EM simulator to study thesystem response of the vias up to 10 GHz. The via model is shown in FIG.19. The model comprises two signal vias (marked as ‘S’ in FIG. 19)surrounded by four ground vias (marked as ‘G’ in FIG. 19). The vias wereexcited with discrete (lumped) ports on their top and bottom surfaces.

The insertion loss and crosstalk between the vias in two types of Siinterposers is compared in FIGS. 20 a and 20 b. TPVs in polycrystallineSi (0.15 Ω-cm resistivity) is compared with TSVs in wafer-based CMOSgrade Si (10 Ω-cm resistivity). The thickness of the Si substrate wasabout 220 μm. The diameter and pitch of these Cu filled vias were about30 μm and about 120 μm, respectively. The TSVs were modeled with about 1μm thick sidewall SiO₂ liner, while the TPVs were modeled with about 5μm thick sidewall polymer liner.

It is observed from FIGS. 20 a and 20 b that the TPVs in polycrystallineSi have lower loss (until about 10 GHz) and lower crosstalk (until about7 GHz) as compared to the TSVs in CMOS grade Si. The better electricalbehavior of the TPVs can be attributed to the thicker polymer linedsidewall and surface liner in these interposers. This helps reduce thesubstrate loss and coupling in the Si substrate.

The effect of the sidewall liner thickness on the insertion loss andcrosstalk in TPVs is studied in FIGS. 21 a and 21 b. The TPV diameterand pitch was about 30 μm (diameter of the Cu filled region) and about120 μm, respectively. The Si substrate resistivity and thickness wasabout 0.15 Ω-cm and about 220 μm respectively. It is seen from FIGS. 21a and 21 b that the insertion loss and crosstalk can be reduced by usinga thicker sidewall polymer liner.

The effect of via diameter on its loss and crosstalk is studied in FIGS.22 a and 22 b. The vias were modeled in about 220 μm thickpolycrystalline Si (0.15 Ω-cm resistivity) with about 5 μm thick polymersidewall liner. The TPV pitch was about 120 μm. The loss in the TPVs canbe reduced by decreasing via diameter. Smaller TPVs have smallersidewall capacitance (due to smaller diameter) and smaller substrateconductance (due to larger spacing between the TPVs). This helps inreducing the loss. Due to the greater spacing between the smaller TPVs,their crosstalk is lower as compared to the larger TPVs.

The performance of TPVs in polycrystalline Si (with thick polymer liner)is better as compared to that of wafer-based CMOS grade Si with thinSiO₂ liner. The electrical performance of the TPVs can be improved bydecreasing its diameter and by increasing the sidewall liner thickness.

Example #2 Mechanical Design of TPVs/TSVs

Finite Element (FE) modeling was performed using Ansys to compare theproposed TPV structure with a polymer liner to the current 3D ICstructure with TSV structure with thin SiO2 liner in terms ofinterfacial shear stresses (σ_(xy)) due to thermal loading. The effectof geometry (liner thickness and via diameter) on the axial stress(σ_(x)) of a polymer liner in TPV structure was also studied.

The material properties used in the simulations are given in Table 3. Astandard thermal load cycle of −55 to 125° C. was used for the analysis.

TABLE 3 Young's Poisson's CTE Stress free Temp. Modulus (GPA) Ratio(ppm/° C.) (° C.) Silicon 185 0.28 2.6 25 Polymer 6.9 0.3 31 120 Copper121 0.3 17.3 25 SiO₂ 70 0.3 0.5 25

The interfacial shear stress localization occurs at the Cu-Polymer(about −90 MPa) and Polymer-Si (about 72 MPa) junctions in the case ofTPV structures, and at Cu—SiO₂ (about 124 MPa) junctions in the case ofTSV structures. The relatively higher interfacial shear stresslocalization in TSV structures can be attributed to the higher CTEmismatch of SiO₂ with Cu vias. This makes the standard Si interposersmore susceptible to delamination failures compared to TPV structuresfabricated with polymer liners. Due to higher stiffness of SiO₂, the TSVstructures are more prone to cohesive cracks compared to TPV structures.It is also expected that TSV structures would experience higher stressduring the back grinding process required for fabricating thesestructures.

Example #3 TPV Fabrication Process

FIG. 23 illustrates the process flow used to fabricate the TPV in apolycrystalline silicon panel.

Example #4 TPV Formation

Several methods for TPV formation in polycrystalline silicon wereexplored as the traditional DRIE processes are too slow to drill TPVs insilicon interposers of about 220 μm thick polycrystalline silicon. Tosolve this problem, TPV formation by laser ablation (UV, excimer andpico-second lasers) was studied. Top and bottom views of the viasfabricated by three types of lasers are compared in FIG. 24.

The UV laser with a wavelength of about 266 nm was faster but resultedin large via entrance diameters ranging from about 75-125 μm. The viaexit diameter (ranging from about 50-100 μm) was smaller than theentrance diameter, indicating significant via taper. The excimer laserwas able to drill smaller vias (about 10-20 μm diameter) than the UVlaser. The excimer laser was able to form nearly vertical TPV sidewallwithout micro-cracking due to minimal thermal damage to the siliconmaterial. Excimer laser processing can be scaled to higher throughput byparallel mask projection ablation. Picosecond lasers can further reducethe heat generated during the laser ablation process. TPVs with about10-50 μm diameter were formed by pico-second laser. However, this methodis currently limited by slow processing speed and serial via formationprocess.

For this initial study, short wavelength UV lasers were chosen for TPVformation in polycrystalline silicon. FIG. 25 shows a typical crosssection picture of a laser ablated through-via in polycrystallinesilicon.

Example #5 Polymer filling and Liner Formation

A novel polymer liner approach is presented to replace the currentcombination of SiO₂ and diffusion barriers used in the processing ofCMOS-based silicon interposers. The technical approach involves polymerfilling of TPV, followed by laser ablation to form an “inner” viaresulting in a via side wall liner of controlled thickness.

The laser drilled silicon samples were first cleaned using a plasmatreatment. About 30 μm thick polymer film was laminated to cover thesurface and fill the TPVs. This was done by an optimized double-sidelamination process with hot press, resulting in void-free fillingwithout cracking the silicon. FIG. 26 shows the optical cross-sectionalimage of polymer laminated silicon substrate with polymer-filled TPV(about 125 μm and about 100 μm via entrance and exit diameterrespectively). Adhesion between polymer and silicon was checked byinitial tape test for peel strength and the samples showed goodadhesion.

UV laser ablation was used to drill through holes in the polymer filledvias. The inner via diameter was controlled to ensure proper sidewallpolymer liner thickness.

Example #6 TPV Metallization

The TPV metallization consisted of two steps: 1) Cu seed layerformation, and 2) Cu electroplating. Electroless plating, a fast, lowcost process, was used in this study to form an about 0.5-1 μm thickcopper seed layer for further electroplating. The polycrystallinesilicon sample with via in polymer was first cleaned using plasma toremove any impurities on the surface. After rinsing the sample, Cu wasplated by electroless deposition on the top and bottom surfaces of thesample, and along the via side wall. A fast, void-free electroplatingwas performed to fill the vias with Cu. Alternate filling methods toimprove the throughput of the via metallization are under investigation.

Example #7 Test Vehicle Fabrication and Characterization

A demonstrator test vehicle was designed and fabricated using theprocess flow diagram as shown in FIG. 27. TPVs were drilled in about 6inch sized polycrystalline silicon panels by using a UV laser. Polymerwas laminated on both sides to fill the via hole. Laser ablation wasperformed in the filled polymer to form the TPV liner. After surfacecleaning, dry film photoresist was laminated on both sides andphotolithography was performed. After patterning the sample, asemi-additive Cu electroplating was performed to fill the TPVs and toform the redistribution layer (about 5 μm thick). Finally, thephotoresist and seed layers were removed sequentially.

Fine line structures were also fabricated on the test vehicle. FIG. 28shows the cross-section picture of the fine line structure on polymerlaminated polycrystalline silicon. The fabrication resulted in fine lineand space features down to about 20 μm.

Co-planar waveguide (CPW) transmission lines were designed andfabricated along with other electrical characterization structures. Thestructures were measured in a VNA after performing SOLT calibrations.

FIG. 29 illustrates the simulation and measurement results of an about6.2 mm long CPW line. It is observed that the transmission lines haveless than 2 dB insertion loss at 9 GHz. This translates to a loss of 0.3dB/mm at 9 GHz.

SINGLE CRYSTAL SILICON INTERPOSER EXAMPLES Example #1 ProcessOptimization, Integration, and Fabrication

TSVS were fabricated on 4″ wafers according to the process flowillustrated in FIG. 34. After cleaning the 400 μm wafer substrate,lithography was performed to pattern the TSV structures using DowChemical SPR220 positive acting photoresist and Karl Suss MA-6 MaskAligner. The recipe for the photoresist was about 1000 rpm/500R/S/5s andthen about 2000 rpm/1000R/S/40s. The average thickness of thephotoresist was about 7.5 μm. After about 35 minutes of baking dry andexposure, the photoresist was developed by using MF-319 developer.

After the lithography process, the sample wafer was attached to a handlewafer and then put into the STS-ICP machine for blind via etching usingBosch Process. In the process of blind via etching, the larger featureshave faster etching and vias with similar dimensions have similaretching speed. For example, after 550 cycles etching in STS ICP, allcircular TSVs with about 65 μm diameter had a similar etch depth ofabout 285 μm compared to about 40 μm circular TSVs with a lower etchdepth of about 260 μm. After blind via etching, back grinding, and finalpolish was used to expose the backside of the vias to form through vias.In order to open the about 40 μm diameter alignment vias on the backside, the wafer was thinned down to about 260 μm. FIGS. 35 a and 35 bshows a typical top and bottom view, respectively, of a circular TSV(about 65 μm) after back grinding and polishing.

Wafer Inspection was also done for about 65 μm via size uniformityacross the wafer (from area 1 and area 2 in the mask layout shown inFIG. 36) and across the five wafers in the batch. The results are shownin Table 4 and uniform via size distribution was observed for both topand bottom sides. However, the diameters of bottom vias are always about8-9 μm larger than the top ones.

TABLE 4 Average Size Top via size (μm) Bottom via size (μm) Difference(μm) Area 1 Area 2 Area 1 Area 2 Bottom-rop Wafer 1 68.35 69.92 77.5977.76 8.45 Wafer 2 67.52 69.5 76.61 77.97 8.1  Wafer 3 68.44 70.39 78.8376.97 9.41 Wafer 4 69.72 69.75 78.1 77.62 8.36 Wafer 5 69 70.22 78.05 798.44

After removing the residual photoresist by using Acetone, a 2 μm thickSiO₂ dielectric isolation layer was deposited by plasma enhancedchemical vapor deposition process at about 250° C. on both sides of thewafer using a Plasma-Therm PECVD or STS-PECVD tool. About 30 nanometer(nm) Ti (barrier for Cu diffusion into SiO₂) and about 1 μm thick copperseed layer were grown on both sides of the sample wafer by using CVC DCSputter to provide the electrical contact for the electroplatingprocess. The sequence of barrier and seed layer sputter deposition forthe through-vias was Ti/Cu sputter on side 1, followed by flipping thewafer and Ti/Cu sputtering on side 2 to get complete coverage on thethrough-via. For high aspect ratio vias, Cu electroless plating processwas used to deposit a thin layer of Cu to ensure complete coverage ofthe metal seed and fix any spots on the via side wall where thesputtered seed layer was not able to reach. A DC electroplating processwas then used to plate copper and fill the TSVs. The holding timebetween seed repair and electroplating was minimized in order to avoidoxidation of Cu and a 10% sulfuric acid clean was performed for about1-2 minutes just before the electroplating step. A current of about 4amps (A) was used for about 8 hours in this process. The final thicknessof the Cu burden on both sides was around 80 μm, which was then thinneddown during the Cu pad formation process.

The Cu pad formation process starts with thinning of the Cu burden bydouble sided micro-etch process using a dilute CuCl₂ solution. Thetarget finished Cu thickness was about 12-15 μm. After thinning the Cuburden, a double-sided lithography process was done using dry filmphotoresist applied to the thin wafer by vacuum lamination. The UVexposure was done with precise alignment using a mask aligner, followedby spray developing using a 1% sodium carbonate solution. The patternedphotoresist mask was used to etch back the Cu by wet etching (CuCl₂chemistry), followed by Ti seed removal using wet or dry etching. Thefinal step in the process sequence was stripping of the photoresistusing a potassium hydroxide solution to result in Cu pad structures.FIG. 37 illustrates the top view and micro-section images of arepresentative TSV daisy chain with about 65 μm diameter vias. Thedefined copper pads for the through vias can be seen on both sides ofthe wafer with a thickness of about 260 μm.

Example #2 Reliability Testing

The first wafer with fully fabricated TSV coupons had a yield of 18working daisy chain coupons of about 65 μm diameter out of a total of 25coupons in the mask layout. Daisy chain resistance was measuredas-fabricated, using both four point and two point probe setups. The twopoint probe setup was used for monitoring the daisy chain resistancethrough thermal cycling. The total resistance of an individual daisychain coupon was measured to be in the range of few ohms, which includesthe resistance of traces on both sides and contact resistance from theprobing in addition to the TSV resistance. JEDEC standard thermal cycletests are in progress from −40° C. to 125° C. after MSL-3preconditioning. Early results from the first 300 cycles indicate somefailures in the periphery of the wafer, while the resistance in theinterior coupons is quite stable.

Numerous characteristics and advantages have been set forth in theforegoing description, together with details of structure and function.While the invention has been disclosed in several forms, it will beapparent to those skilled in the art that many modifications, additions,and deletions, especially in matters of shape, size, and arrangement ofparts, can be made therein without departing from the spirit and scopeof the invention and its equivalents as set forth in the followingclaims. Therefore, other modifications or embodiments as may besuggested by the teachings herein are particularly reserved as they fallwithin the breadth and scope of the claims here appended.

We claim:
 1. A three-dimensional (3D) glass interposer interconnectstructure, comprising: a glass interposer having a first side and asecond side, the glass interposer being 20 microns to 100 microns inthickness; and a plurality of through-vias defined within the glassinterposer extending at least from the first side to the second side ofthe glass interposer; wherein the glass interposer electrically connectsfirst and second electronic devices on either side of the through-viasand has the same or substantially the same through-via interconnectdensity as the first and second electronic devices it connects; andwherein the plurality of through-vias are 3 microns to 50 microns inpitch and 1 micron to 25 microns in diameter.
 2. The interconnectstructure of claim 1, wherein the first electronic device is attached tothe first side of the glass interposer and the second electronic deviceis attached to the second side of the interposer.
 3. The interconnectstructure of claim 1, further comprising a plurality of blind vias and aplurality of conductor traces defined within a redistribution layer onthe first side and the second side of the glass interposer, wherein theblind vias and conductor traces enable the interposer to electricallyconnect to first and second electronic devices of different input/output(I/0) pad layouts and sizes.
 4. The interconnect structure of claim 1,wherein the first and second electronic devices communicate at abandwidth of at least 10 GB/s.
 5. The interconnect structure of claim 1,wherein the first and second electronic devices communicate at abandwidth of at least 12 GB/s.
 6. The interconnect structure of claim 1,wherein the through-vias are metalized.
 7. The interconnect structure ofclaim 6, wherein the through-vias are metalized with copper.
 8. Theinterconnect structure of claim 6, wherein the through-vias aremetalized with a low coefficient of thermal expansion (CTE) conductivealloy.
 9. The interconnect structure of claim 6, wherein thethrough-vias are metalized with a thick polymer liner.
 10. Theinterconnect structure of claim 6, wherein the through-vias aremetalized with a seeding metal liner for subsequent electroplating. 11.The interconnect structure of claim 1, wherein the first electronicdevice is a logic device.
 12. The interconnect structure of claim 1,wherein the second electronic device is a memory device.
 13. Theinterconnect structure of claim 1, wherein the glass interposer is 20 to50 micrometers in thickness.
 14. The interconnect structure of claim 1,wherein the plurality of through-vias are 1 to 20 micrometers indiameter.
 15. The interconnect structure of claim 1, wherein theplurality of through-vias are 3 to 30 micrometers in pitch.
 16. Theinterconnect structure of claim 1, wherein the first and secondelectronic devices are connected to the glass interposer in aface-to-face configuration.
 17. The interconnect structure of claim 1,wherein the first and second devices are electrically connected to padsor through-vias on the first and second sides of the glass interposer,respectively, using solder, copper bumps with solder caps,copper-to-copper bonding, adhesive bonding, metallurgical bonding,non-conductive bonding, or combinations thereof.
 18. The interconnectstructure of claim 1, wherein at least one of the first and secondelectronic devices does not comprise through-vias.
 19. The interconnectstructure of claim 1, further comprising: a third and fourth electronicdevice, wherein the third and fourth electronic devices are stacked onthe first and second electronic devices, respectively, in athree-dimensional (3D) configuration; and wherein the first and secondelectronic devices comprise a plurality of through-vias to electricallycommunicate with the third and fourth electronic devices, respectively.20. The interconnect structure of claim 1, wherein the glass interposeris a large panel.
 21. A testable glass interposer interconnectstructure, comprising: a glass interposer having a first side and asecond side, the glass interposer being 20 microns to 100 microns inthickness; and a plurality of through-vias defined within the glassinterposer extending at least from the first side to the second side ofthe glass interposer; wherein the glass interposer electrically connectsfirst and second electronic devices on either side of the through-viaand has the same or substantially the same through-via interconnectdensity as the first and second electronic devices it connects; whereinthe glass interposer comprises test pads on the first and second sidesof the glass interposer to enable testing of electronic devices attachedand electrically connected to at least one of the first and second sidesof the glass interposer; and wherein the plurality of through-vias are 3microns to 50 microns in pitch and 1 micron to 25 microns in diameter.22. The interconnect structure of claim 21, wherein electrical packagetest methods are applied to verify the functioning of the glassinterposer, the glass interposer with the first electronic device on thefirst side of the glass interposer, followed by the second electronicdevice mounted on the second side of the glass interposer.
 23. Athermally-manageable glass interposer interconnect structure,comprising: a glass interposer having a first side and a second side,the glass interposer being 20 microns to 100 microns in thickness; and aplurality of through-vias defined within the interposer extending atleast from the first side to the second side of the glass interposer;and wherein the glass interposer electrically connects first and secondelectronic devices on either side of the through-via and has the same orsubstantially the same through-via interconnect density as the first andsecond electronic devices it connects; wherein either the first or thesecond electronic devices have exposed surfaces for bonding thermalheatsinks or other thermal structures and are connected by a pluralityof electrically and thermally conducting through-vias, wherein theplurality of through-vias are distributed within the glass interposerand provide localized thermal isolation or thermal conduction betweenthe first and second electronic devices; and wherein the plurality ofthrough-vias are 3 microns to 50 microns in pitch and 1 micron to 25microns in diameter.
 24. The interconnect structure of claim 23, whereinthe glass interposer provides thermal conduction in X and Y planedirections.
 25. A scalable glass interposer interconnect structure,comprising: a glass interposer having a first side and a second side,the glass interposer being 20 microns to 100 microns in thickness; and aplurality of through-vias defined within the glass interposer extendingat least from the first side to the second side of the glass interposer;wherein the glass interposer electrically connects electronic devicesand has the same through-via interconnect density as the electronicdevices it connects; and wherein a plurality of electronic devices areattached to the first side of the glass interposer in a side-by-sideconfiguration; and wherein the plurality of through-vias are 3 micronsto 50 microns in pitch and 1 micron to 25 microns in diameter.
 26. Theinterconnect structure of claim 25, wherein a plurality of electronicdevices are attached to the second side of the glass interposer in aside-by-side configuration.